This invention relates to compositions for plugs of refractory materials used to plug the tapholes of blast furnaces, and especially to a binding material which is a component in the compositions.
In the operation of blast furnaces, it is custormary to retain molten material within the furnaces by plugs of refractory material which have been inserted into discharge orifices or "tapholes" of such furnaces in a plastic condition and then allowed to harden, so as to form an integral portion of the furnace retaining wall. When it is desired to withdraw the molten material from the furnace, the refractory plug must be broken and removed.
Generally speaking, "mud" is the term used to refer to the compositions of refractory material for plugs. However, in the present specification, that term will not be used. Rather, the term, "composition for refractory plugs" will be used.
To date, the material used to plug the tapholes of blast furnaces, that is, the composition for refractory plugs, has consisted of a composite of at least one refractories aggregate and at least one binding material. The refractories aggregates which have been used are clay, chamotte, pyrophyllite (roseki), alumina, zircon, silicon carbide and similar materials, and the principal materials which have been employed as binders are tars such as anhydrous tar, tar for pavement, cutback tar (converted tar) as well as pitch and athracene.
The greatest advantage of employing tars, pitch or similar materials is mainly due to their plasticity and resistance to corrosion. These tars, however, tend to harden and become so hard that if a long period of time elapses from the mixing of the above compositions for taphole materials until the actual operation of the furnace, is becomes impossible to extrude these compositions from the applicator or extruder, which is called a "mud gun". Consequently, undesirable phenomena which are referred to as "extrusion incapability" are apt to occur and result in a condition of unstable operation of the furnace. Furthermore, tars which are used as binders of the compositions for refractory plugs are heated to such an extent that they begin to burn during the operation of the furnace and generate a yellowish black smoke which is bad smelling and is a source of pollution not only of the area surrounding the blast furnace but also of the atmosphere, that is, it is a source of environmental pollution. In addition to this problem, laborers who come in contact with the tars or the vapors thereof during the mixing of the above compositions for refractory plugs or during the operation of the blast furnaces suffer from inflammation of the skin, which is a significant safety problem in the working conditions of the factory. Also, tars are designated by law as specific chemical materials which require circumspection in manufacturing processes due to their polluting qualities and it is necessary that great care be taken when handling them.
In order to overcome these defects, compositions for refractory plugs which compositions contain plastics as binding materials have been advocated. However, most plastics which are used as binding materials are aromatic compounds and when burned they may release volatile constituents which are said to be harmful to health. Therefore, the problem of pollution has not yet been completely eliminated.
With this background, the present invention is intended to solve problems encountered in the routine operation of blast furnaces as well as to eliminate environmental pollution.
Thus, it is an object of this invention to provide improved compositions for refractory plugs used to plug the tapholes of blast furnaces which compositions do not readily stiffen even after the lapse of a long period of time without being used.
Another object of this invention is to provide improved compositions for refractory plugs used to plug the tapholes of blast furnaces which compositions will not cause environmental pollution which occurs when conventional compositions for refractory plugs are burned during the service of the furnace.
The improved compositions for refractory plugs in accordance with the present invention are characterized by the use of a specified amount of at least one petroleum pitch which has a high softening point and is used as the binder and a specified amount of at least one alcohol selected from the group consisting of dihydric alcolhols and polymers thereof and is used as the agent which imparts workability or plasticity to the composition; these constituents are mixed with a refractories aggregate which has a conventional proportion and range of particle sizes.
Other objects and advantages of the invention will readily become apparent by a thorough consideration of a preferred embodiment thereof.